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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>
        // 第八题
        var a = 10;
        function test() {
            a = 100;
            console.log(a); // a =100;
            console.log(this.a); // a =10;
            var a;
            console.log(a);// a ==100
        }
        test();
    </script>
</body>

</html>